1. Field of the Invention
The present invention relates to an ink-jet head for forming an image on a print surface by ejecting droplets of ink. The present invention also relates to an ink-jet printer including an ink-jet head.
2. Description of the Related Art
An ink-jet head and an ink-jet printer including the ink-jet head are known in which pressure chambers are arranged along one flat face of a flat passage unit, and each pressure chamber is connected to a nozzle open in the other flat face of the flat passage unit, nozzle open face, and to a common ink chamber, manifold passage, disposed within the passage unit (see U.S. Patent Application No. 2001/0020968). In such an ink-jet head, in general, an actuator unit is bonded to the passage unit to cover the open face of each pressure chamber. The actuator unit includes a piezoelectric element. By the piezoelectric effect obtained by the piezoelectric element, the volume of each pressure chamber is changed to eject ink through the corresponding nozzle.
In the above-described ink-jet head, the common ink chamber provided within the passage unit preferably has a cross section, perpendicular to the ink flow, as large as possible in order that each pressure chamber is smoothly and evenly supplied with ink and thereby a good ejection performance is obtained. On the other hand, in the passage unit and the ink-jet head including the passage unit, reduction in size and a highly dense arrangement of nozzles are required. Therefore, if reduction in size of the passage unit and a highly dense arrangement of nozzles are intended to be realized with suppressing a decrease in the cross section of the common ink chamber, the distance from the nozzle open face to the bottom face of the common ink chamber, that is, the thickness of the bottom wall of the common ink chamber, cannot help being decreased.
On the other hand, in the ink-jet printer, for the purpose that ink in each nozzle is prevented from being dried and/or air contained in ink are discharged with the ink, the nozzles of the ink-jet head are covered with a rubber cap when printing is not performed. An annular protrusion, refered to as a “lip”, provided on the cap is brought into contact with the nozzle open face of the passage unit with a relatively large force to isolate the nozzles from the outside air. Therefore, if the distance from the nozzle open face to the bottom face of the common ink chamber is small, that is, the bottom wall of the common ink chamber is thin, the bottom wall of the common ink chamber may be concaved by the capping force applied from the cap to the passage unit.
To prevent this, the profile of the lip may be designed such that the lip to surround the nozzles is not brought into contact with the bottom wall of the common ink chamber in the nozzle open face. In this design, even if the lip strongly presses the passage unit, the bottom wall of the common ink chamber is scarcely influenced by the capping pressure and less likely to be deformed.
The position of the lip to be in contact with the passage unit may deviate from the designed position because of a positional error in assembling the printer. For this reason, a certain distance is necessary between the inner edge of the lip and the periphery of the nozzles. However, if the distance between the inner edge of the lip and the periphery of the nozzles is too large, the outer edge of the lip is close to the bottom wall of the common ink chamber. Hence, even if a slight positional shift occurs, the lip may press the bottom wall of the common ink chamber. To prevent this, the distance between the common ink chamber and the nozzles in a plan view must be increased. In this measure, however, the external shape of the ink-jet head increases in size.